The spinal disc plays a key role as part of the ‘spinal motion unit’ enabling both movement and allowing the spine to function as a suspension system. Each unit enables a degree of movement and cushioning such that forces can be dissipated throughout the length of the spin. The disc works in combination with two facet joints at each spinal level forming a movement segment which enables and allows e.g. flexion / extension at the lumbar spine.

The disc structure comprises two end plates above and below with a central nucleus containing a soft, gelatines material. This nucleus is surrounded and is encased in a tuff multilayered annulus fibrosis. When pressure is applied to the disc it functions as a hydraulic unit, reducing in height, deforming  temporarily as the gel is pressed out in to the anulus. The elastic recoil then returns the disc to its original height and shape.

Injury to the disc can result in a nucleus gel contents, moving out of the disc, backwards towards the spinal cord. Contact with the nerve tissue (in the spinal cord) results in an inflammatory response and symptoms typically seen with Sciatica / nerve route irritation. Prolapsed discs most commonly develop at the lower part of the lumbar spine between the last lumbar vertebrae (L5) and the scrum often termed L5 / S1.